More Doubts Over The Oxytocin And Trust Theory

By Neuroskeptic | September 16, 2015 9:20 am

The claim that the hormone oxytocin promotes trust in humans has drawn a lot of attention. But today, a group of researchers reported that they’ve been unable to reproduce their own findings concerning that effect.

The new paper, in PLoS ONE, is by Anthony Lane and colleagues from Louvain in Belgium. The same team have previously published evidence supporting the link between oxytocin and trust.

Back in 2010 they reported that “oxytocin increases trust when confidential information is in the balance”. An intranasal spray of oxytocin made volunteers more likely to leave a sensitive personal document lying around in an open envelope, rather than sealing it up, suggesting that they trusted people not to peek at it.

However, the authors now say that they failed to replicate the 2010 ‘envelope task’ result in two subsequent studies.

Here’s the key data. The original 2010 results are at the top, the two replications are below. The bars show the proportion of participants who left the envelope sealed and taped (least trusting), sealed only, or open (most trusting).


Participants given oxytocin (green) were much more trusting in the original study compared to those on placebo (blue). However in the replications, this effect was absent.

Lane et al. conclude that

The non-significant results of these two failed replications clearly exclude a large effect of oxytocin on trust in this paradigm… Taken together, our results question the purported size of oxytocin’s effect on trust and emphasize the need for replications.

But then, why did the original study find such a large effect? Lane et al. point out that it’s extremely unlikely that the original effect was just a fluke: the effect size in the 2010 study was enormous, and the effect was highly significant at p<0.001.

Instead, the authors suggest that the effect may have been driven by ‘unconscious behavioral priming’. The 2010 study was only single-blind – the participant didn’t know whether they were getting oxytocin or placebo but the experimenter did know. The researchers might have behaved differently towards the participants based on that knowledge. Plausibly, this could have made the participants feel more or less comfortable. The replications were double-blind and so were immune to this bias. So maybe that was the problem all along.

There’s one odd feature of the data, however: in the replications, people on placebo were much more trusting than in the original study. In the original, almost everyone in the placebo group sealed and taped the envelope, but in both of the replications, hardly anyone did that. This difference is unexplained, and Lane et al. don’t discuss it. Die-hard oxytocin-trust believers might complain that the null results are ceiling effects although I don’t think this is the case because there is still plenty of “room” for oxytocin to increase trust.

Either way, we should applaud Lane and colleagues for being willing to question their own results – and for being brave enough to run a direct replication of their own results in the first place (and so face the risk of ‘failure’).

ResearchBlogging.orgLane A, Mikolajczak M, Treinen E, Samson D, Corneille O, de Timary P, & Luminet O (2015). Failed Replication of Oxytocin Effects on Trust: The Envelope Task Case. PloS ONE, 10 (9) PMID: 26368396

  • Rolf Degen

    Wouldn’t it be a bit more precise to call the presumed confounder “Experimenter’s bias”, or, more specifically, ” observer-expectancy effect” (which can even occur in animals, think “Clever Hans”), than to conjure up ‘unconscious behavioral priming’, which seems to be so hard to replicate by itself?

    • Neuroskeptic

      Agreed. Although I don’t think they are invoking “priming” in the technical sense of say “Professor priming“.

      I think they mean that the experimenters were behaving differently without intentionally doing so.

  • Uncle Al

    unable to reproduce their own findings” “p<0.001

    If it quacks like psychology, walks like psychology, has feathers and webbed feet and associates with psychologists — I’m certainly going to assume that it is fraudulent. The original paper is behind a paywall. Was it NIH funded, the father of all intent and the mother of no real world results?

    Was Clever Hans a co-author?

    • stormchaser1983

      there are just too many variables in science…assuming no fraud, it is possible that an experimental outcome might have many plausible underlying reasons…thats how science progresses, by refining knowledge of the ground truth. best example i can give of this fact is quantum refining einstein refining newton.

  • Filip

    Hi, interesting post. But about your “odd feature of the data”, is it really odd? Don’t you think that the bias suggested by the authors is meant to also explain the placebo-group behavior? You write, “Plausibly, this could have made the participants feel more or less comfortable.” I guess that the experimenters in the first study unknowingly suppressed trusting behavior among placebo-sprayed people by making them “less comfortable”.

    • Nacho Sanguinetti

      I agree, I think it makes sense. It is reasonable to assume that the experimenter effect is going both ways, making Oxy subjects feel more comfortable (hence pushing distribution to the right) and making Placebo subjects feel less open (pushing distribution to the left). When the experimenter stops being able to do this (blind) then both distributions go back to normal and apparently normal means no difference for this paradigm.

      • Neuroskeptic

        Yeah, that’s true.

  • Rolf Degen

    In the discussion of the original paper, the researchers explicitly stressed that they found the influence of an experimenter’s bias unlikely, given that the verbal contact with the experimenter was limited – most instructions were given by the computer – and instructions were fully standardized.

    • Neuroskeptic

      Oh! Well spotted.

      In the new paper they say

      “The third hypothesis suggests that the effect of OT that we found in the original study does not truly exist but that we artificially created it. In our original study, OT administration followed a single blind procedure. As demonstrated by Doyen et al. the experimenter who knows the participants’ condition may unintentionally act differently so that participants’ behavior may be altered to confirm the researcher’s hypothesis. Because the original, single blind, study is the only one in which we obtained an effect of OT on the envelope task, we cannot formally exclude that the significant at the .05 level effect was the product of unconscious behavioral priming.”

      They don’t mention their previous assurances.

    • LeoB

      It is unclear to me if the contact with the experimenter is the same in the replication as in the original study.

      The experimenter might be influenced by the contact with the participants. A participant on OT may behave differently than a participant on placebo. This non-verbal communication then comes back from the experimenter to the participant. (Another way to break the blind!)

  • Leonid Schneider

    Indeed, now at the replication stage the placebo made people significantly more cautious. Which makes no sense, thus we are safe to assume all these experimental setups are bunk and produce stochastic pseudo-significant effects which may go either way. Should the Science article be retracted, if its science isn’t reliable anymore? Nah. Arsenic bacteria are also doing well, Science-wise.

    • Rolf Degen

      “Stochastic pseudo-significant effects” reminds me of the tips Diederik Stapel allegedly got from his colleagues early in his “career”. Which, if true, speaks volumes:

      “Don’t do this test on a computer. We tried that and it doesn’t work. It only works if you use pencil-and-paper forms.”
      “This experiment only works if you use ‘friendly’ or ‘nice’. It doesn’t work with ‘cool’ or ‘pleasant’ or ‘fine’. I don’t know why.”
      “After they’ve read the newspaper article, give the participants something else to do for three minutes. No more, no less. Three minutes, otherwise it doesn’t work.”
      “This questionnaire only works if you administer it to groups of three to five people. No more than that.”

  • Paul Bocken

    Were the participants told (before or during experiment) that the
    experiment was about trust and chemicals? Implicit knowledge, based on
    media-coverage of ‘neuroscience’ that ‘there exists some stuff that
    enhances trust’ might explain the rise of placebo-effect.

  • gia jo

    Seriously? How about the theory that Oxy just mellows the person so that they just don’t think about the envelope or don’t care? Duh….

    • Elizabeth_Reed

      Are you thinking of Oxycontin? That’s a very different substance…

      • Neuroskeptic

        Indeed. Although it has also been claimed that oxytocin reduces anxiety…

        • Elizabeth_Reed

          Sure, but “reducing anxiety” isn’t quite the same as mellowing someone out to the point that they lose concern for an envelope that contains a “sensitive personal document.” The latter sounds like it describes getting high, which is definitely *not* an effect of oxytocin (at least not to my knowledge). It would be interesting if oxytocin made people apathetic or forgetful in the way that, e.g., smoking pot does, only without the unmistakable subjective effects and observable changes in demeanor, affect, etc. I doubt that’s the case, though.

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  • practiCalfMRI

    Anyone know anything about the placebo properties or whether oxytocin has a detectable odor or taste when administered intranasally? Route of admin was flagged by Quintana et al. as a possible cause of variable response. See blue highlighted section here: But one must always look at the control very carefully and ensure it really is a good control.

    • Herve Cadiou

      As far as I know oxytocin is odorless although it has some effects on the olfactory epithelium itself. No I can think of two factors which could have come into play: Inflammation and summer/winter cycles.

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  • ohwilleke

    Not your discipline, but the professional ethical questions should be familiar, and you so rarely get an opportunity to point the finger at physicists that it is noteworthy.

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  • Awesomedogs

    Thanks for posting an article involving replication. Such an important concept to avoid the “bright, shiny, sexy new science thing” that often happens.

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Neuroskeptic is a British neuroscientist who takes a skeptical look at his own field, and beyond. His blog offers a look at the latest developments in neuroscience, psychiatry and psychology through a critical lens.


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